问题 单项选择题

三鹿牌等不合格婴幼儿奶粉中掺入了一种“假蛋白”——三聚氰胺。图为三聚氰胺分子的结构式。下列有关“假蛋白”的说法正确的是()

A.三聚氰胺可与双缩脲试剂发生紫色反应

B.三聚氰胺中氮元素的含量比碳元素的含量还高

C.在奶粉中添加三聚氰胺后提高了蛋白质的含量

D.三聚氰胺分子中含有三个肽键

答案

参考答案:B

解析:

考查蛋白质的结构和性质。蛋白质可与双缩脲发生紫色反应,由图中结构式可看出,三聚氰胺不是蛋白质,不含肽键,因此不能与双缩脲发生紫色反应,故A项、D项错误;由所给结构式粗略计算可知,三聚氰胺中氮元素的含量高于碳元素的含量,在奶粉中添加三聚氰胺可增加氮元素的含量,但其本身并非蛋白质,因此并不能提高奶粉中蛋白质的含量,故C项错,B项正确。

阅读理解

B

If you have a bottle of water recycled from urine(尿), would you drink it? Astronauts at the ISS may soon do so.

NASA(美国航空航天局)said it would see a high-tech machine to recycle wastewater at the ISS. The machine will recycle water for washing hands, shower water, water for brushing teeth and even urine to make drinking water. It will save millions of dollars each year.

At present, each ISS astronaut uses about 4.4 liters of water every day. It costs about 24 million dollars a year to send water up to the ISS. A liter of water costs about $11,000.

The machine will be sent to the ISS later. NASA hopes it will recycle about 93% of all the water used on the station.

Will the water be clean? Different chemicals will be put in the wastewater. The water will be heated to 130℃ to kill bacteria. Scientists say that the recycled water is thousands of times better than the water from a city tap(水龙头).

50. NASA will use a high-tech machine to recycle wastewater at the ISS to ______.

A. protect the ISS                            

B. make the astronauts work harder

C. provide better water and food for the astronauts  

D. save the cost of sending water up to the ISS

51. At present it costs NASA about ___dollars to transport water up to an astronaut at the ISS a day.

A. 4.4 thousand       B. 11 thousand              C. 48.4 thousand                  D. 24 million

52. The passage mainly tells us something about ______.

A. water recycling at the ISS      B. the International Space Station

C. a high-tech machine                D. the cost of NASA

53. Which of the following sentences is TRUE?

A. The recycled water is much better than that from a city tap.

B. The high-tech machine will recycle all the water used on the station

C. The ISS astronauts use more water than us

D. The high-tech machine can only recycle urine to make water

单项选择题